For testing blood, interstitial fluid or other body fluids, it is customary to use test elements carrying test fields with reagents that effect a detection reaction when exposed to a body fluid sample. The detection reaction, for example, can lead to fluorescence or a color change that can be analyzed by photometry to determine an analyte concentration such as the concentration of glucose, lactate or hematocrit. Also known are detection reactions for electrochemical measurements of an analyte concentration. In either case, the detection reaction leads to a change in a parameter that can be measured physically, whereby the intensity of the change depends on the analyte concentration to be measured.
Typically, detection sensitivity varies substantially between production batches of test elements containing the reagents. For this reason, there is a need to have calibration data to be able to determine the analyte concentration with high precision when analyzing the result of the detection reaction from the extent of the change of the physical parameter such as a change of color. Calibration data of this type usually is determined for each production batch using calibration liquids of known analyte concentration. The calibration data is stored on a data carrier that is jointly distributed with the test element. The user or patient then transfers the calibration data to a measuring device. This often leads to higher complexity of the overall process, lower compliance by the patient and is prone to error and manipulation.
Such calibration data also allows using test elements with different reagents or detection reactions for concentration measurements of different bodily fluids such as blood, blood plasma, serum, urine, saliva, semen, lymph, synovial fluid, amniotic fluid, lacrimal fluid, cyst fluid, sweat or bile with respect to a broad variety of analytes, such as glucose, lactate, hematocrit, cholesterol or peptides.
An approach to circumvent the need for calibration data is to optimize production with regard to tolerances, which is usually unfavorable with respect to production cost and leads to large amounts of rejections. The calibration data can contain the information that is necessary to determine the analyte concentration from the result of the detection reaction.
EP Patent Application Publication No. 1574855 describes a system having a barcode containing calibration information that is fixed to the outside of a drum cartridge containing several test elements. It also is known to print barcodes directly on test elements. An important aspect of barcode-based data storage disclosed in the document is that the drum magazine has to be located precisely to avoid reading errors.
Although optical data storage by means of a barcode is inexpensive, the reading process of barcodes is prone to errors. This is especially true for analytical test elements where users handle the test elements, which may impair barcodes by fingerprints or scratches. In the best case, an error may be detected and the reading process repeated. Conversely, and in the worst case, erroneous calibration data is used that may cause incorrect measurement results. Moreover, standard barcode readers are rather large and require either a movement of the barcode or a scanning optic for a reading process.
Int'l Patent Application Publication No. WO 2008/151726 discloses cartridges carrying electronic or magnetic data storages such as electrically erasable programmable read-only memory (EEPROMS), radio-frequency identification (RFID) tags, smartcards or memory chips. With these storage devices, calibration data stored therein can be more reliably retrieved. However, this advantage is offset by higher costs and impractical for consumables for single use such as, for example, single test elements. For the foregoing reasons, additional means of storing and retrieving information such as calibration data on an analytical consumable are needed.